<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8" />
    <title>CSS发光立体</title>
    <link rel="stylesheet" href="style.css" />
  </head>
  <body>
    <div class="box">
      <div class="top"></div>
      <div>
        <span style="--n: 0"></span>
        <span style="--n: 1"></span>
        <span style="--n: 2"></span>
        <span style="--n: 3"></span>
      </div>
    </div>
  </body>
</html>
